An injection-molding machine commonly comprises a machine bed on which a pair of mold-carrying plates can be provided, a fluid-pressure-operated cylinder arrangement for displacing at least one of these plates toward and away from the other in a mold-opening and mold-closing direction and for holding the mold closed between these plates during the injection at elevated pressure of a synthetic resin or plastics material which then sets in the mold cavity to form an object.
The object is generally ejected upon opening of the mold, i.e. retraction of the mold-carrying plate or platens with or without the use of an ejection mechanism with which the machine may be equipped.
One or both of these mold-carrying plates can be provided with one or more apertures communicating with a source of the flowable but settable material, e.g. a cylinder in which one or more worms can plastify the synthetic resin material and which may be axially movable or provided with a ramp to drive the flowable material through the aforementioned passage or passages in the mold-carrying plate into the mold cavity.
The machine can also be provided with conventional service facilities, e.g. fluid circuitry for circulating lubricants or coolants through the mold or into the various parts.
It is customary to make one of the mold-carrying plates stationary while the other is movable and is guided on, say, four circular-section guide bars which properly align the two mold-carrying plates. The conventional approach also individually secures the two halves of a separable mold to the respective mold-carrying plates. More specifically, the mold may consist of two or more parts which are separated and which, when brought together, will define the mold cavity. These parts are customarily and hereinafter referred to as mold halves even if additional mold parts are provided and either part makes up more or less than a true geometric half of the mold herein.
In the injection-molding field, considerable down-time of an injection-molding machine has frequently been considered endemic since mold-changing operations were fairly complex. Mold-changing operations are involved when one must replace a damaged or worn mold or when one wishes to substitute a different product for the product previously manufactured by the machine. The dismounting of the mold part from its mold-carrying plate was a complex and time-consuming ordeal as was the connection of the various service fittings to the mold and the resetting of machine controls to accommodate the new mold and its cavities.
Because injection-molding machines are generally operated with high output rates, a down-time which is even comparatively small may result in a substantial drop in productivity. Hence systems for the rapid change of the mold, i.e. quick-change mold systems are of interest. A quick-change mold system requires a rapid locking arrangement which can quickly secure a mold part to a mold-carrying plate.
Thus, the Ludwig Engel KG Maschinenfabrik, A-4311 Schwertbach, Austria, has described in the prospectus Engel-Information A-67-TV-9/81 a rapid attachment device for securing each of the mold halves to the respective mold-carrying plates or platens of an injection-molding machine of the type described, thereby reducing the down-time.
A significant disadvantage of this system, however, is that it nevertheless requires a number of traction bolts to be used to secure the mold heads to the mold-carrying plates and hence time-consuming screwing operations. Another disadvantage of this system is that the bolts used for mounting, centering and alignment must project beyond the base of the mold halves, thereby requiring a considerable span between the mold-carrying plates adapted to receive the mold. This may require larger means than may be necessary. A corollary problem, also resulting from the large gap between the mold-carrying plates, is that the centering and attachment operations require considerable replacement of at least one of the mold-carrying plates, a factor which has been found to contribute to imprecision in alignment.
Finally, we should take note of the fact that prior-art devices for changing molds in an injection-molding machine generally include cranes and like lifting or hoisting appliances to enable the massive mold structure to be moved from its position between the platens, to be carried away and to be replaced with another mold. When the new mold is suspended from such a hoist, it is difficult to properly align the bolts with the bores of the mold-carrying plate as a result of the swing of the hoist and the load suspended therefrom.